As it is known, in a turbine blading, along the height of each aerofoil, variation of the load exerted by the primary gas flow (the load is proportional to the difference in pressure between the pressure side and the suction side) in general is imposed as a linear interpolation trend between the load conditions at the two opposite ends of the aerofoil.
Recently, load distributions with a parabolic trend rather than a linear trend have been proposed and adopted, so as to decrease the load (and therefore the difference in pressure between the pressure side and the suction side) in proximity of the endwalls, and the radial ends of the blading.
In fact, this tends to limit the secondary flows losses in the boundary layer at the endwalls, as the higher the difference in pressure in the interblade channel between pressure side and suction side is, the higher the boundary layer and corresponding secondary flow losses become.
A schematic illustration of the phenomenon of secondary flow generation in an interblade channel is indicated in FIG. 1. The secondary flows are essentially generated by the difference in pressure between the pressure and suction sides of the two adjacent blades and flow along the boundary layer in circumferential direction in proximity of the endwalls: therefore, they are orthogonal to the direction of the primary gas flow in the interblade channel. These flows in circumferential direction generate a flow also along the pressure and suction sides of the two adjacent blades, again orthogonal to the direction of the primary gas flow.
As mentioned above, it has been attempted to limit secondary flow losses in the turbine blading by reducing the difference in pressure between pressure side and suction side: in fact, this tends to reduce the thrust that leads to the generation of flows in circumferential direction inside the boundary layer close to the endwalls in the interblade channel.
The various proposals relating to “Side Wall Contouring” technologies of non axisymmetric type, i.e. relating to non-circular shape of the endwalls, have also had the same objective and focus.